Safe inks employed in ink-jet printers generally contain water soluble dyes which are not very smear resistant after drying on paper.
Printing of colored ink on paper using ink-jet printing is known. See, for example, Savit, U.S. Pat. No. 4,382,262. In that patent, drops of clear material are fired onto a specially treated paper, which combines with material in the paper to form colored dots. Several jets are employed; each jet is connected to a reservoir containing a different colorless material, which upon contact with the specially treated substrate chemically reacts to provide a different color.
U.S. Pat. No. 4,360,548 provides a hidden image, made detectable by rubbing, by applying to a substrate a first ink-like material in image configuration, followed by a second ink-like material to cover the image and the area surrounding the image. Each of the two materials contain one of a color-forming pair of reactants which are substantially colorless, but which together react to form a colored product.
Neither of these references discloses nor suggests forming smear-resistant inks on a substrate. Thus, a need remains for a simple method for improving the water fastness of the ink on a substrate.